A.B.
Divorce is hard, especially on the children. When dad can't come around, for whatever reason, the child may feel that he isn't loved anymore or that something he did caused the split. I am a big proponent of being mature in a divorce and realizing that you aren't the only one that was hurt. I know parents who have continually blamed the other spouse in front of their children. I even knew teenagers who were told after the split that daddy didn't want them or love them anymore. While it might make mommy feel safer and more secure in the child's love, it makes the child feel unloved, unwanted, and insecure. I'm not saying that's your situation, I'm just letting you know what the child may be feeling right now.
The best thing to do is be as honest as possible, telling them what is happening as far as they can understand what you are telling them. A 12 year old will understand what divorce means, and he may even understand more than you think. The best thing to do would be to explain kindly that mommy and daddy aren't living together anymore. If daddy chooses not to visit, you might explain that daddy is so busy getting his new life in order that he doesn't have a lot of time (or it's too far to travel often) but that he still loves the child. If daddy can't have visitation because of bad choices, you could also explain that daddy is having a hard time right now, and not making good choices. Explain that while daddy loves his child, he needs some time to get his life together and make better choices before he comes to visit. Whatever the reason, don't place blame or get angry. Make sure that the child knows that daddy and mommy both love him/her and that daddy will come to visit as soon as he can. Remind him that while daddy may be gone for a little while, you are still there and will always be there.